There are on the market a great number of various small hand-held mobile stations in which a battery can be used as a power supply. Previously, it was used mainly Ni--Cd (nickel-cadmium) batteries which were quite big and heavy, compared with their capacity. Lately they are being replaced by Ni--MH (nickel-metal hybrid) batteries and Li--Ion (lithium-ion) batteries, the capacity of which, as to size and weight, is better than that of Ni--Cd batteries. Simultaneously, the development of semiconductor technology has resulted in more compact mobile stations with lower power consumption, and it has been possible to further reduce the size of the batteries used in them.
As the thickness of the batteries used in mobile communication devices and other corresponding small devices has been reduced at its lowest to just a few millimetres, even the space required by their casing has changed from an insignificant factor to a more and more important element in regard with the size of a battery-operated device. In the first stage the thickness of battery walls could be reduced due to the reduced need of mechanical support because of the batteries being lighter, out of economic reasons, but in the newest and smallest devices it has been possible to choose even new materials and advanced manufacturing processes in order to minimize the size of the final product. In patent application publication EP 795 968 there is provided a solution for making the battery walls thinner, in which solution two of the plastic walls normally enveloping the battery cells are manufactured from thin steel foil. A construction made using two different materials is, however, slightly problematic in regard to the production technology and also in regard to the recycling at the end of the life span of the product. Additionally, if the metal surface remains visible on the outside of the product, its looks may differ from the otherwise plastic case of the product in an embarrassing way.
Thanks to the developments in battery and semiconductor technologies it has been possible to reduce the size of battery operated mobile stations without compromising the operating times of the devices. In spite of that it is desired to manufacture the future mobile stations even smaller and lighter, because they are intended to be continuously carried by their users. Of these devices particularly problematic in regard to the use of space are two-part folding devices of the PDA (Personal Digital Assistant) type, such as Nokia Communicator. It is difficult to reduce the thickness of such a device integrating the functions of a PDA and a mobile station, because inside the covers of a folded device there must be room for at least one, but preferably two displays, a keyboard comprising preferably a complete set of characters, the electronics of a mobile station and that of a PDA, and a battery. Yet, the keyboard should be large enough to be good to use and that in order to present the purposes of the keys the corresponding symbols can be printed in connection with the keys. An additional problem in integrating a PDA and a mobile station is that the power consumption normally is higher than that of only one of these and a battery facilitating a sufficient operating time is reasonably big. Naturally the same problem concerns also other hand-held devices, such as PDA-equipment, wireless telephones, mobile and wireless telephones provided with a flap, palmtop computers and laptop computers. It has been attempted make such devices thinner by designing the electronics to take up as little space as possible and by manufacturing the covers of the product as thin as possible whenever it can be done. For example, when using injection moulding technique the minimum thickness of a plastic component is determined by the flowing properties in a mould of the melted plastics, and when the flow-channel inside a mould is small enough, the plastics will no longer fill it and in such a point there will be a hole instead of a thin wall.
Further, devices sold in large series to consumers have to be provided with a marking of their origin and they are often provided with an individual serial number, by using which it is possible to track the manufacturing date and the machine among other things in order to avoid the misuse of warranty service and to make the detection of piratism easier. This has often been implemented by attaching in the case of a device a sticker, in which the required product data has been printed. A sticker is, however, exposed to wear and damage and it is relatively easy to forge into a pirate product.